Effects of isoproterenol and propranolol on the inducibility and frequency of ventricular fibrillation in patients with Brugada syndrome

SCN5A-C683R exhibits combined gain-of-function and loss-of-function properties related to adrenaline-triggered ventricular arrhythmia

NEW FINDINGS

What is the role of SCN5A-C683R? SCN5A-C683R is a novel variant associated with an uncommon phenotype of adrenaline-triggered ventricular arrhythmia in the absence of a distinct ECG phenotype. What is the main finding and its importance? Functional studies demonstrated that Na_V 1.5/C683R results in a mixed electrophysiological phenotype with gain-of-function (GOF) and loss-of-function (LOF) properties compared with Na_V 1.5/wild type. Gain-of-function properties are characterized by a significant increase of the maximal current density and a hyperpolarizing shift of the steady-state activation. The LOF effect of Na_V 1.5/C683R is characterized by increased closed-state inactivation. Electrophysiological properties and clinical manifestation of SCN5A-C683R are different from long-QT-3 or Brugada syndrome and might represent a distinct inherited arrhythmia syndrome.

ABSTRACT

Mutations of SCN5Ahave been identified as the genetic substrate of various inherited arrhythmia syndromes, including long-QT-3 and Brugada syndrome. We recently identified a novel SCN5A variant (C683R) in two genetically unrelated families. The index patients of both families experienced adrenaline-triggered ventricular arrhythmia with cardiac arrest but did not show a specific ECG phenotype, raising the hypothesis that SCN5A-C683R might be a susceptibility variant and the genetic substrate of distinct inherited arrhythmia. We conducted functional cellular studies to characterize the electrophysiological properties of Na_V 1.5/C683R in order to explore the potential pathogenicity of this novel variant. The C683R variant was engineered by site-directed mutagenesis. Na_V 1.5/wild type (WT) and Na_V 1.5/C683R were expressed in tsA201 cells. Electrophysiological characterization of C683R was performed using the whole-cell patch-clamp technique. Adrenergic stimulation was mimicked by exposure to the protein kinase A activator 8-CPT-cAMP. The impact of β-blockers was tested by exposing Na_V 1.5/WT and Na_V 1.5/C683R currents to propranolol and nadolol. C683R resulted in a co-association of gain-of-function and loss-of-function properties of Na_V 1.5. Gain-of-function properties were characterized by a significant increase of the maximal Na_V 1.5 current density compared with Na_V 1.5/WT (861 ± 309 vs. 627 ± 489 pA/pF; P < 0.05, n ≥ 9) that was potentiated in Na_V 1.5/C683R with 8-CPT-cAMP stimulation (869 ± 287 vs. 607 ± 320 pA/pF; P < 0.05, n ≥ 12). C683R also resulted in a significant hyperpolarizing shift in the voltage of steady-state activation (-65.4 ± 3.0 vs. -57.2 ± 4.8 mV; P < 0.001), resulting in an increased window current compared with WT. The loss-of-function effect of Na_V 1.5/C683R was characterized by significantly increased closed-state inactivation compared with Na_V 1.5/WT (P < 0.05). C683R is a novel SCN5A variant resulting in a co-association of gain-of-function and loss-of-function properties of the cardiac sodium channel Na_V 1.5. The phenotype is characterized by adrenaline-triggered ventricular arrhythmias. Electrophysiological properties and clinical manifestations are different from long-QT-3 or Brugada syndrome and might represent a distinct inherited arrhythmia syndrome.

2019 HRS/EHRA/APHRS/LAHRS expert consensus statement on catheter ablation of ventricular arrhythmias

Ventricular arrhythmias are an important cause of morbidity and mortality and come in a variety of forms, from single premature ventricular complexes to sustained ventricular tachycardia and fibrillation. Rapid developments have taken place over the past decade in our understanding of these arrhythmias and in our ability to diagnose and treat them. The field of catheter ablation has progressed with the development of new methods and tools, and with the publication of large clinical trials. Therefore, global cardiac electrophysiology professional societies undertook to outline recommendations and best practices for these procedures in a document that will update and replace the 2009 EHRA/HRS Expert Consensus on Catheter Ablation of Ventricular Arrhythmias. An expert writing group, after reviewing and discussing the literature, including a systematic review and meta-analysis published in conjunction with this document, and drawing on their own experience, drafted and voted on recommendations and summarized current knowledge and practice in the field. Each recommendation is presented in knowledge byte format and is accompanied by supportive text and references. Further sections provide a practical synopsis of the various techniques and of the specific ventricular arrhythmia sites and substrates encountered in the electrophysiology lab. The purpose of this document is to help electrophysiologists around the world to appropriately select patients for catheter ablation, to perform procedures in a safe and efficacious manner, and to provide follow-up and adjunctive care in order to obtain the best possible outcomes for patients with ventricular arrhythmias.

2019 HRS/EHRA/APHRS/LAHRS expert consensus statement on catheter ablation of ventricular arrhythmias

Ventricular arrhythmias are an important cause of morbidity and mortality and come in a variety of forms, from single premature ventricular complexes to sustained ventricular tachycardia and fibrillation. Rapid developments have taken place over the past decade in our understanding of these arrhythmias and in our ability to diagnose and treat them. The field of catheter ablation has progressed with the development of new methods and tools, and with the publication of large clinical trials. Therefore, global cardiac electrophysiology professional societies undertook to outline recommendations and best practices for these procedures in a document that will update and replace the 2009 EHRA/HRS Expert Consensus on Catheter Ablation of Ventricular Arrhythmias. An expert writing group, after reviewing and discussing the literature, including a systematic review and meta-analysis published in conjunction with this document, and drawing on their own experience, drafted and voted on recommendations and summarized current knowledge and practice in the field. Each recommendation is presented in knowledge byte format and is accompanied by supportive text and references. Further sections provide a practical synopsis of the various techniques and of the specific ventricular arrhythmia sites and substrates encountered in the electrophysiology lab. The purpose of this document is to help electrophysiologists around the world to appropriately select patients for catheter ablation, to perform procedures in a safe and efficacious manner, and to provide follow-up and adjunctive care in order to obtain the best possible outcomes for patients with ventricular arrhythmias.

2019 HRS/EHRA/APHRS/LAHRS expert consensus statement on catheter ablation of ventricular arrhythmias

Ventricular arrhythmias are an important cause of morbidity and mortality and come in a variety of forms, from single premature ventricular complexes to sustained ventricular tachycardia and fibrillation. Rapid developments have taken place over the past decade in our understanding of these arrhythmias and in our ability to diagnose and treat them. The field of catheter ablation has progressed with the development of new methods and tools, and with the publication of large clinical trials. Therefore, global cardiac electrophysiology professional societies undertook to outline recommendations and best practices for these procedures in a document that will update and replace the 2009 EHRA/HRS Expert Consensus on Catheter Ablation of Ventricular Arrhythmias. An expert writing group, after reviewing and discussing the literature, including a systematic review and meta-analysis published in conjunction with this document, and drawing on their own experience, drafted and voted on recommendations and summarized current knowledge and practice in the field. Each recommendation is presented in knowledge byte format and is accompanied by supportive text and references. Further sections provide a practical synopsis of the various techniques and of the specific ventricular arrhythmia sites and substrates encountered in the electrophysiology lab. The purpose of this document is to help electrophysiologists around the world to appropriately select patients for catheter ablation, to perform procedures in a safe and efficacious manner, and to provide follow-up and adjunctive care in order to obtain the best possible outcomes for patients with ventricular arrhythmias.

Pharmacological Therapy in Brugada Syndrome

Brugada syndrome (BrS) is a cardiac disease caused by an inherited ion channelopathy associated with a propensity to develop ventricular fibrillation. Implantable cardioverter defibrillator implantation is recommended in BrS, based on the clinical presentation in the presence of diagnostic ECG criteria. Implantable cardioverter defibrillator implantation is not always indicated or sufficient in BrS, and is associated with a high device complication rate. Pharmacological therapy aimed at rebalancing the membrane action potential can prevent arrhythmogenesis in BrS. Quinidine, a class 1A antiarrhythmic drug with significant Ito blocking properties, is the most extensively used drug for the prevention of arrhythmias in BrS. The present review provides contemporary data gathered on all drugs effective in the therapy of BrS, and on ineffective or contraindicated antiarrhythmic drugs.

The roles of pacing interval and pacing strength in ventricular fibrillation induced by rapid pacing with 1 : 1 capture

INTRODUCTION

The roles of pacing interval (PI) and pacing strength (PS) in ventricular fibrillation (VF) induced by rapid pacing with 1 : 1 capture remain unclear.

MATERIAL AND METHODS

Epicardial unipolar electrograms (UEs) were simultaneously recorded using contact mapping in 11 swine. Activation-recovery interval (ARI) restitution was constructed at 4 sites, i.e. the apex and base of the left and right ventricles, respectively. A steady state pacing (SSP) protocol was performed to induce VF. The longest PI and the lowest PS for inducing VF were recorded. Statistical correlation analysis was performed to determine the relationship between local ARI restitution properties and PI and PS for VF induction.

RESULTS

Forty restitution curves were constructed from 11 SSP procedures. The maximal slope (Smax) of the ARI restitution curve of the right ventricular apex was positively correlated with the PI for VF induction (r = 0.761, p < 0.05). Spatial dispersions of ARI and Smax were negatively correlated with the PS for VF induction (r = -0.626 and r = -0.722, respectively, both p < 0.05).

CONCLUSIONS

Ventricular fibrillation can be induced by rapid ventricular pacing with 1 : 1 capture. The PI for VF induction was related to the Smax of the ARI restitution curve of the right ventricular apex, while PS for VF induction was associated with the spatial dispersions of ARI and its restitution property.

Circulating heart-type fatty acid-binding protein levels predict ventricular fibrillation in Brugada syndrome

BACKGROUND

The association between ongoing myocardial damage and outcomes in patients with Brugada syndrome who had received an implantable cardioverter-defibrillator (ICD) is unclear.

METHODS

Consecutive patients with Brugada syndrome (n=31, 50±13 years) who had received an ICD were prospectively enrolled. Minor myocardial membrane injury [heart-type fatty acid-binding protein (H-FABP) >2.4ng/mL] and myofibrillar injury (troponin T >0.005ng/mL) were defined using receiver operating characteristic curves. Patients were followed for a median period of 5 years to an endpoint of appropriate ICD shock.

RESULTS

Myocardial membrane injury (29%) and myofibrillar injury (26%) were similarly prevalent among patients with Brugada syndrome who had received ICDs. Appropriate ICD shocks occurred in 19% of patients during the follow-up period. Multivariate Cox regression analysis showed that serum H-FABP level >2.4ng/mL, but not troponin T level, was an independent prognostic factor for appropriate ICD shock due to ventricular fibrillation [hazard ratio (HR) 25.2, 95% confidence interval (CI) 1.33-1686, p=0.03].

CONCLUSIONS

Evaluating myocardial damage using H-FABP may be a promising tool for predicting ventricular arrhythmia in patients with Brugada syndrome who have received ICDs.

Sodium channels, cardiac arrhythmia, and therapeutic strategy

Cardiac sodium channels are transmembrane proteins distributed in atrial and ventricular myocytes and Purkinje fibers. A large and rapid Na(+) influx through these channels initiates action potential and thus excitation-contraction coupling of cardiac cells. Cardiac sodium channel is composed of a pore-forming α-subunit and one or two accessory β-subunits. The cardiac α-subunit is encoded by gene SCN5A located on chromosome 3p21. There are four types of β-subunits identified so far, and β1 is the primary β-subunit in cardiac Na(+) channels. The gene responsible for β1 subunits is SCNB. The expression of β-subunits together with α subunits enhances the Na(+) current and modifies the channel activities. In addition, interactions of the cardiac Na(+) channel with other proteins may facilitate the channel activity and membrane expression of the channel. Over the past two decades, molecular genetic studies have identified the linkage of gene mutations of the Na(+) channel proteins and other regulatory proteins to many inherited arrhythmogenic diseases. The most common cardiac arrhythmogenic diseases associated with Na(+) channelopathies are long QT syndrome (LQT3) and Brugada syndromes (BrSs). This chapter intends to summarize the current understanding of the normal sodium-channel structure and function, the gene mutation-associated cardiac arrhythmias, and the current diagnosis and management of these diseases.

Brugada syndrome: an update

More than 20 years have passed since the description of Brugada syndrome as a clinical entity. The original case series depicted patients who all had coved ST-segment elevation in the right precordial leads, associated with a high risk of sudden death and no apparent structural heart disease. As subsequent registry data were published, it became apparent that the spectrum of risk is wide, with the majority of patients classified as low risk. Two consensus documents have been published that will continue to be updated. Despite intense research efforts, many controversies still exist over its pathophysiology and the risk stratification for sudden death. Management continues to be challenging with a lack of drug therapy and high complication rates from implantable cardioverter defibrillators. In this review, we highlight the current state-of-the-art therapies and their controversies.

Donepezil-induced torsades de pointes without QT prolongation

We report a case of torsades de pointes (TdP) induced by donepezil without QT prolongation. An 86-year-old woman was admitted to our hospital because of a syncopal attack. She had been treated for Alzheimer's disease with donepezil. Initial 12-lead electrocardiogram showed atrial fibrillation and normal corrected QT interval. After admission, atrial fibrillation spontaneously recovered to normal sinus rhythm on electrocardiographic monitoring. On the second day, electrocardiographic monitoring documented TdP. We discontinued donepezil immediately. After washout of donepezil, TdP was not observed again. Corrected QT interval was normal throughout hospitalization. This case suggests that donepezil may cause life-threatening ventricular arrhythmias without QT prolongation. Even if corrected QT interval is normal in patients taking donepezil and experiencing symptoms associated with TdP, electrocardiographic monitoring is recommended. .

Sinus node disease in subjects with type 1 ECG pattern of Brugada syndrome

BACKGROUND

The spectrum of phenotypes related to mutations of the SCN5A gene include Brugada syndrome (BS), long QT syndrome, progressive cardiac conduction defect, and sinus node disease (SND). The present study investigated the incidence of SND in subjects with type 1 electrocardiogram (ECG) pattern of BS.

METHODS AND RESULTS

The study population consisted of 68 individuals (55 males, mean age 44.8±12.8 years) with spontaneous (n=27) or drug-induced (n=41) type 1 ECG pattern of BS. Twenty-eight subjects were symptomatic with a history of syncope (41.2%). SND was observed in 6 symptomatic subjects (8.8%), and was mainly attributed to sino-atrial block with sinus pauses. Two patients were initially diagnosed with SND, and received a pacemaker. Patients with SND displayed an increased P-wave duration in leads II and V2, PR interval in leads II and V2, QRS duration in leads II and V2, and increased QTc interval in lead V2 (p<0.05). AH and HV intervals as well as corrected sinus node recovery time (cSNRT) were significantly prolonged in subjects with SND (p<0.05). During a mean follow-up period of 5.0±3.6 years, five subjects with a history of syncope suffered appropriate implantable cardioverter defibrillator (ICD) discharges due to ventricular arrhythmias (7.4%). None of those diagnosed with SND suffered syncope or ICD therapies.

CONCLUSION

SND is not an uncommon finding in subjects with type 1 ECG pattern of BS. The occurrence of SND in relatively young patients may deserve meticulous investigation including sodium channel blocking test.